Omega-3 fats linked to lower diabetes risk

NEW YORK (Reuters Health) - People who get plenty of omega-3 fatty acids in their diets may have lowered odds of developing type 2 diabetes, two new reports suggest.

In one study, of more than 3,000 older U.S. adults, researchers found that those with the highest blood levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) -- two omega-3s found in fatty fish -- were about one-third less likely to develop diabetes over the next decade than their counterparts with the lowest levels.

In the other, researchers found that among 43,000 Singapore adults, those who got the most alpha-linolenic acid (ALA) in their diets had a decreased diabetes risk. ALA is an omega-3 fat found in certain plant foods, including flaxseed, canola oil and soy.

But before anyone runs out to buy fish oil pills, researchers caution that their findings do not prove that omega-3 fats, themselves, fight diabetes. The fats may, for instance, be markers for some other aspect of the participants' diet or lifestyle that influences diabetes risk.

People often hope there is a dietary "magic bullet" against disease, noted Andrew Odegaard of the University of Minnesota in Minneapolis, one of the researchers on the Singapore study.

He advised that people focus on getting plenty of healthy "whole foods" -- especially fruits, vegetables, fiber-rich grains, legumes, vegetable oils and fish -- instead of any single nutrient.

"Approaching your dietary intake with this 'big picture' approach should take care of the small things, like essential nutrients such as omega-3 fatty acids," Odegaard told Reuters Health in an email.

Neither of the new studies, which appear in the American Journal of Clinical Nutrition, proves that omega-3s directly lower diabetes risk.

In fact, studies up to now have come to conflicting conclusions on the connection between omega-3s and diabetes. A few have even found that people with a high intake of omega-3s, which are considered "good" fats, have an increased diabetes risk.

But the new U.S. study did something most previous ones have not: looked at people's actual blood levels of omega-3 fatty acids and their later risk of diabetes.

That type of study generally offers stronger evidence than those which ask people about their eating habits.

Researchers led by Dr. Luc Djousse of Harvard University used information on 3,088 older U.S. adults taking part in a heart-health study. At the outset, participants' blood levels of EPA, DHA and ALA were measured. Over the next decade, 204 were diagnosed with diabetes.

The researchers found that of the one-quarter of study participants with the highest EPA/DHA levels, 5 percent developed diabetes. That compared with 6.5 percent of the one-quarter with the lowest blood levels of the fatty acids.

The difference was greater when it came to ALA levels: just under 4 percent of people with the highest levels developed diabetes, versus 8.5 percent of those with the lowest.

When the researchers accounted for other factors -- like weight and exercise habits -- people's omega-3 levels, themselves, were still connected to a lower diabetes risk.

For the other study, Odegaard and his colleagues looked at records from 43,176 Singapore adults ages 45 to 74 who were interviewed about their diet habits, then followed over the next decade. During that time, 2,252 developed diabetes.

Overall, the 20 percent of participants with the highest ALA intake from food were less likely to develop diabetes than the 20 percent who ate the least: just under 5 percent did, versus 6 percent in the lowest-intake group.

After accounting for weight, exercise and other factors, the researchers found that high ALA intake was linked to a 22 percent dip in diabetes risk.

Omega-3s from fish, however, were not tied to diabetes risk.

It's not clear why ALA appeared to protect against diabetes, according to Odegaard. Some lab research, he said, has suggested that omega-3s -- and particularly ALA -- might improve body cells' sensitivity to insulin, the hormone that regulates blood sugar.

However, Odegaard also pointed out that people who consume a lot of ALA are likely to have a good diet overall -- and probably healthy lifestyle habits like regular exercise.

And while he and his colleagues tried to factor in those variables, it's still possible that it is not the ALA, specifically, that offers the anti-diabetes benefit.

As for why omega-3 from fish was not linked to diabetes risk, Odegaard said that a potential explanation might rest in how people prepare their fish. If it's fried and served with less-than-healthy side dishes, for example, any protective effect of omega-3s might be washed out.